Mosunetuzumab has a favorable benefit-to-risk ratio in patients with relapsed or refractory follicular lymphoma (FL), according to researchers.

Mosunetuzumab produced a complete response (CR) rate of 60%, and the median duration of CR was not reached. Cytokine release syndrome (CRS) was the most common adverse event (AE), but it was mostly grade 1 or 2 in severity.

These results, from an ongoing phase 2 trial ( Identifier: NCT02500407), were reported in The Lancet Oncology.

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The trial included 90 patients with relapsed or refractory FL who had a median age of 60 (range, 53-67) years. The patients had received a median of 3 lines of prior therapy. All patients previously received an alkylator and anti-CD20 therapy, and 53% of patients were refractory to both.

Patients received mosunetuzumab in 21-day cycles with cycle 1 step-up dosing: 1 mg on cycle 1 day 1, 2 mg on cycle 1 day 8, 60 mg on cycle 1 day 15 and cycle 2 day 1, and 30 mg on day 1 of cycle 3 and onward. Patients received a median of 8 treatment cycles, and the median follow-up was 18.3 months. 

The primary endpoint was CR rate as assessed by an independent review committee. The CR rate was 60%, which was significantly higher than the 14% CR rate historically seen with copanlisib (P <.0001). 

The objective response rate was 80%. Late responses did occur, with 38% of patients demonstrating deepening of their initial response and 31% achieving a CR after more than 8 cycles of mosunetuzumab. The median duration of response was 22.8 months, and the median duration of CR was not reached.

The median progression-free survival was 17.9 months, and the median overall survival was not reached.

The most common AE was CRS, which occurred in 44% of patients. CRS was mostly grade 1 or 2 (42%) in severity. One patient developed grade 3 CRS, and 1 had grade 4 CRS. 

The most common grade 3-4 AEs were neutropenia (27%), hypophosphatemia (17%), hyperglycemia (8%), and anemia (8%). There were no treatment-related grade 5 AEs. 

“The overall benefit-to-risk ratio of mosunetuzumab in patients with relapsed or refractory follicular lymphoma and two or more previous therapies appears favorable and will be further validated in ongoing studies,” the researchers wrote.

A phase 3 trial is underway to evaluate mosunetuzumab plus lenalidomide and rituximab in patients with relapsed/refractory FL ( Identifier: NCT04712097).

Disclosures: The phase 2 study was supported by F Hoffmann-La Roche and Genentech. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


Budde LE, Sehn LH, Matasar M, et al. Safety and efficacy of mosunetuzumab, a bispecific antibody, in patients with relapsed or refractory follicular lymphoma: A single-arm, multicentre, phase 2 study. Lancet Oncol. Published online July 5, 2022. doi:10.1016/S1470-2045(22)00335-7